The present invention relates to an electrolytic device suitable for use in a liquid chromatographic system.
Suppressed ion chromatography is a known technique for analysis of sample ions of one charge in an eluent containing electrolyte. First, the sample ions in the eluent are chromatographically separated. Then, the eluent is suppressed by removal of the electrolyte counterions to the sample ions, and the sample ions are detected, typically by an electrical conductivity detector. One type of suppressor device, called a sandwich membrane suppressor, is described in U.S. Pat. No. 4,999,098 (the “'098 patent”). In one embodiment, the suppressor includes three channels. During suppression, the eluent and separated sample ions flow through the central channel of the suppressor while regenerant solution flows in the two outside channels. The outside two channels are separated from the central channel by barriers having exchangeable ions capable of passing ions of only one charge, positive or negative, and of blocking bulk liquid flow. Suitable barriers are ion-exchange membranes sold under the trademark Nafion®. One embodiment is an electrolytic, three-channel flat membrane suppressor illustrated in FIGS. 2 and 3 of the '098 patent. For an anion analysis, the eluent including the analyte anions which have been previously separated on a chromatographic column, comprising a packed bed of anion exchange resin, flows through the central channel. The ion-exchange membranes include exchangeable cations. Eluent cations are removed from the central channel and are drawn toward the negative electrode across the adjacent membrane barrier, as illustrated in FIG. 3 of the '098 patent. Thus, if sodium hydroxide is used as the electrolyte of the eluent, the sodium ion is removed from the central channel across the cation exchange membrane adjacent to the cathode. A three-channel device of this type has also been used for purposes other than suppression such as pretreatment of a liquid sample prior to chromatographic separation.